[MUSIC PLAYING] We are the Association for Child and Adolescent Mental Health, or ACAMH for short, and this is ACAMH Learn. [MUSIC PLAYING] Hello, everyone. My name is Dr. Robert Eves. I'm the first author on the recently published paper in JCPP, anthropometric differences between twins at birth and their association with later cognitive performance. There are quite a lot of studies finding an association between relatively low birth weight and reduced cognitive performance later in life. There are also alternative metrics, such as head circumference that have been less frequently used, but also been shown to show an association. However, infants of differing birth weight or head circumference may differ on many other things that are important for development, including genetics and family socioeconomic factors. We therefore wanted to investigate whether the association between anthropometrics at birth and cognitive performance is confounded by genetics and family factors. In order to investigate this, we use data from twins. Monozygotic twins are particularly interesting because they are matched on many, many important things, genetic growth potential, genetic IQ potential, they have the same gestational age, and they grow up in largely similar environments. Crucially, however, they can differ on anthropometrics at birth, and this is an indication of the effectiveness of the placenta for each twin. We specifically use data from twin life, which is a longitudinal study of twins from Germany. It comprises both monozygotic and dizygotic twins, and we had neonatal information coming from the U-Heft book, which is doctor reported information on gestational age, birth weight, and head circumference. We also then had cognitive performance that was measured much, much later when participants were on average 12 years at wave 1 or about 18 years at wave 4. We used the co-twin control model, which is a specific type of linear mixed model where we break down differences in birth weight both between twin pairs and within twin pairs. And within twin pair difference in something such as relative birth weight or head circumference is our main independent variable. If this variable is associated with later cognitive performance, it's a very strong indicator that cognitive performance is influenced by conditions in the womb as we control for genetics and family socioeconomic factors. In our main analysis, we had approximately 2,000 twin pairs, and we found that within twin pair difference in birth weight z-score was significantly associated with later cognitive performance. In addition, when we tested for moderation by things such as zygosity, we found no significant effect. In some, this would suggest that the association between birth weight z-score and later cognitive performance is not confounded by genetic or family socioeconomic factors. In contrast, we found no significant association between within twin pair differences in head circumference and later cognitive performance. It was also not moderated by zygosity. However, one thing to note is that in comparison to our analyses with birth weight, we had a much, much reduced sample at approximately 684 twin pairs. Our results suggest that being the smaller twin in regards to birth weight is associated with reduced cognitive performance and suggests that conditions in the womb has a quasi-causal effect on cognition. In contrast, and potentially surprisingly, head circumference differences were not associated with differences in IQ. However, twins are, on average, more preterm and have lower relative birth weights. And maybe we shouldn't even expect results to be similar to those in the general population because of these reasons. There are a couple of limitations to keep in mind. We had a limited sample size for some of the models, and we appeared to lack statistical power, and we also did not know whether twins shared a placenta or not, which may be a crucial factor. Thank you very much for listening, and I hope you will read the full paper now published in JCPP. [MUSIC PLAYING]